1. Technical Field of the Invention
The present invention relates generally to temperature stabilization techniques using passive devices. More particularly, the present invention relates to an apparatus and method for stabilizing a battery compartment""s temperature, which battery compartment is provided for housing backup battery or batteries in a cabinet along with other electronic or telecommunications equipment and circuitry.
2. Description of Related Art
Various types of cabinets, housings, enclosures, etc. (collectively xe2x80x9chousingsxe2x80x9d) are used to house equipment and circuitry. In the field of telecommunications industry, it is common practice to house network equipment and circuitry in a cabinet or enclosure that is required to meet certain environmental and reliability standards. More often, the equipment and circuitry housed in the cabinet use power generated from a backup battery or batteries, typically disposed in a lower portion of the cabinet, in order to remain in operating condition during utility power outages. Accordingly, it is necessary to maintain the batteries"" temperature at a relatively constant level in order to prolong their service life and ability to provide backup power during power outages.
It is known that the capacity of the batteries to provide backup power and current decreases with decreasing ambient temperature within the cabinet. Further, during operation and charging, batteries emit potentially explosive hydrogen gas and its byproducts, which must be evacuated from the cabinet. In order to evacuate the hydrogen gas and its byproducts from the cabinet, a constant flow of air through the battery compartment is necessary. Some of the existing solutions that address these concerns include operating fans or blower mechanisms to draw in outside air in an effort to remove the hydrogen gas from the cabinet. However, these solutions are not satisfactory because in the process of removing the noxious gases and byproducts, the battery compartment is exposed to outside temperatures, and during winter months, this exposure causes the batteries to quickly lose their capacity.
Thus, there is a need not only to evacuate the hydrogen gas emitted into the cabinet during operation of the batteries, but also to maintain the batteries at a uniform temperature irrespective of the changes in the ambient temperature. Known solutions to warm the batteries during colder ambient temperatures include utilizing electrically powered heater pads or radiant heaters (generally referred to as heating devices). However, these solutions are also beset with various shortcomings and deficiencies. First, heating devices require large amounts of AC electricity to generate the resistive heating required to stabilize battery temperatures during colder ambient temperature periods. Consequently, during power outages, such devices are of little use. Further, the heating devices must be operated in an open ambient environment in order to avoid the risk of sparking the potentially explosive hydrogen gas generated during operating cycles of the batteries.
Based on the foregoing, it should be appreciated that there has arisen an acute need for a method and apparatus for stabilizing the temperatures of a battery in a passive manner, thus preventing the risk of sparking the potentially hydrogen gas and its byproducts that could be generated during the operating cycles of the battery. Furthermore, it is required that such a solution be capable of stabilizing the temperature of the batteries even during AC power outages.
Accordingly, the present invention is directed to an innovative solution which provides for the stabilization of battery or battery compartment""s temperature by alternating airflow through an internal ductwork of a cabinet used for housing electronic equipment and circuitry in addition to backup battery or batteries. Ambient air is drawn through one or more intake vents or louvers provided with the cabinet housing. Regulated airflow through the ductwork allows the cabinet housing""s thermal management system to direct either cooler ambient air during warm periods or heated air during colder periods through the cabinet""s battery compartment to stabilize the battery temperature as well electronics equipment and circuitry housed in the cabinet. At least a portion of the heated air inside the cabinet housing is expelled via one or more exhaust vents provided with the housing. Because no active components are used for stabilizing battery temperature, thermal regulation is achieved even during utility power outages. Further, thermal energy is provided without the possibility of igniting hydrogen gas products generated by the battery units present in the cabinet.
In one aspect, the present invention is directed to a battery temperature stabilization system which includes a housing having one or more intake vents and one or more exhaust vents for receiving and expelling air, respectively. A plurality of air passage ways are provided in the housing for circulating air to an electronic equipment compartment and a battery compartment disposed in the housing. The battery compartment includes at least one battery operable to provide backup power to circuitry disposed in the electronic equipment compartment. At least one heat exchanger unit is provided in the housing for transferring heat generated from electronic equipment compartment into a ductwork chamber forming a portion of the air passage ways. A plurality of dampers are provided for controlling the amount of air flow through the air passage ways and the intake/exhaust vents. In one embodiment, an air conducting unit is included in addition to or in lieu of the dampers for routing the drawn in ambient air through the ductwork chamber in one of two directions. The ambient air is first heated or warmed (i.e., thermally conditioned) by the heat exchanger before being directed to the battery compartment when the battery compartment""s temperature is lower than ambient temperature. Otherwise, the ambient air is directed to flow in proximate contact with the battery compartment prior to receiving heat from the heat exchanger, thereby cooling the battery compartment.
In another exemplary embodiment of the present invention, the air conducting unit is comprised of a bi-directional fan operable to blow air in two directions. In yet another exemplary embodiment, two separate fans which are independently energized may be provided as the air conducting unit, wherein one fan is operable to blow air in one direction and the other fan operates to blow air in the opposite direction. In the presently preferred exemplary embodiments, the dampers are provided as bimetallic spring operated units that are preferably thermostatically controlled.
In another aspect, the present invention is directed to a method of passively stabilizing temperature within an enclosure including an electronic equipment compartment and a backup battery compartment. First, a select amount of ambient air is drawn into the enclosure through an intake vent. If the temperature of the battery compartment or the enclosure is greater than a select temperature, the ambient air is circulated in proximate contact with the battery compartment prior to directing the ambient air via a ductwork chamber to a heat exchanger. Preferably, the heat exchanger operates to transfer heat generated in the electronic equipment compartment. By routing cooler ambient air directly, the battery compartment""s temperature in warmer ambient conditions is accordingly regulated. Otherwise, where the temperature of the battery compartment or the enclosure is lower than a predetermined temperature, the ambient air is directed via the ductwork chamber to the heat exchanger for warming the ambient air. The warmed ambient air is thereafter circulated in proximate contact with the battery compartment in order to maintain the battery compartment""s temperature in cooler ambient conditions. Preferably, at least a portion of warmed ambient air may be removed from the enclosure through an exhaust vent.